The Centers for Disease Control and Prevention has estimated that 1.7 million nosocomial infections occur annually in the U.S. with 99,000 associated deaths. The reduction of such infections forms an important component of efforts to improve healthcare safety. Many of these infections originate from “natural flora” bacteria or fungi that have developed immunity to traditional disinfection and antibiotic regimens. Research has shown that relevant infectious flora demonstrate significant susceptibility to select wavelengths of visible light in the presence of oxygen and can be substantially reduced with practical exposure powers and time. Methods for preventing/reducing infections are needed due to the increased flora resistance to antibiotic and conventional disinfection.
Several types of patients are at risk of infection. There is a high correlation of surgical patients with nosocomial infections. Compromised skin due to implant, surgical, catheter or needle penetration and subsequent covering of the resultant wound with light-blocking bandages provides a high-risk vector site for infection by light-sensitive pathogenic microbes, such as Methicillin-resistant Staphylococcus aureus (MRSA). Other types of wounds at high risk for infection include, for example, burns, and chronic diabetic ulcers, among others.
Prior art devices implementing the medicinal use of light on skin include multiple light and/or radiation emitting sources and associated electrical connectivity incorporated into a bandage or other material directly at the site of the wound. These are problematic for application to a fresh or chronic open wound site. Such devices lack provisions for the required sterility. In particular, organic light emitting diodes (OLED) are subject to degradation when exposed to sterilizing agents, such as gamma radiation, steam or Ethylene Oxide. Incorporating light sources directly into the bandage material is cost prohibitive, and ill-suited for a disposable bandage. In addition, the proximity of the light/radiation emitters to the wound presents a challenge to conducting heat generated by the light/radiation emitters away from the patient. Further, locating OLEDs in the proximity of the wound may be problematic as OLEDs generally have a reduced service life in high humidity conditions.
The wiring used for electrical connectivity between the light/radiation emitters and a power source present risks such as exposing the patient to electrically energized components and to electromagnetic fields, which may be of particular concern to surgical patients with other electromechanical medical devices, such as pace makers. Supplemental oxygen used in adjunct medical therapy may further be susceptible to ignition. By using a lightguide to move the radiation emitter remote from the patient these concerns can be addressed.
Lightguides include physical media that conveys light introduced to an ingress portion of the media to an egress portion of the media some distance apart from the ingress portion. The physical media is an optically conducting media such as a clear glass or plastic. A common optically conducting media is an optical fiber. Another form of lightguide is a transparent plate or film, where the ingress and/or egress portion is an edge of the plate of film. Such a lightguide is called an edge lit film.
When light traveling in an optically conducting medium reaches a boundary having an angle larger than the critical angle for the boundary, the light is completely reflected. This is called total internal reflection (TIR). The TIR of an optical fiber confines light within the optical fiber. Light travels through the fiber, bouncing back and forth off the boundary between the fiber and fiber surface. Only light that enters the fiber within a certain range of angles can travel down the fiber without escaping. Disturbing the surface of a fiber creates a region where some of the conducted light escapes the fiber. These areas are called dispersion areas.
Similarly, the TIR of an edge lit film confines light within the edge lit film. The TIR of the edge lit film may be disturbed in several ways, for example, bending the film beyond a TIR threshold, or disturbing the surface of the edge lit film by several methods, including scoring or laminating a substance with different optical properties. An edge lit film may not emit any visible light from its planar surface if that planar surface is not disturbed. For example, a substantially transparent edge lit film may appear transparent and unlit even when conducting light through it if the planar surface is not disturbed.
Flexible light producing films have been used in several applications, for example, back illumination for displays and control panels. FIG. 1A shows a first prior art flexible light producing panel 1 formed by assembling many individual optical fibers together into an aligned sheet. A group 10 of individual fibers extends from the panel, and is bundled into a light cable 11 formed of the individual fibers. The light cable 11 is attached to a light source 14 by a connector 12. The light cable 11 conveys light from the light source 14 to the light panel 1.
As shown by FIG. 1B, individual optical fibers 5 may be interleaved, for example, woven, to form one or more thin light emitting layers 3,4 of a light producing panel. Alternatively, individual fibers 5 may be aligned substantially in parallel.
As shown by FIG. 1C, The planar surface 2 of the light emitting panel 1 may be disrupted, for example by scoring the planar surface, to cause light to be emitted from the disrupted surface of the fibers rather than being transmitted to the end of each fiber. However, the process of forming a large number of individual fiber optic strands into a panel is complex and costly.
A second prior art light producing panel or film is formed from a single sheet of edge lit light conducting material having a TIR so that it contains and conducts light in a fashion similar to a fiber optic cable. Light may be dispersed from the surface of the panel by disturbing the surface of the panel, similarly to the light fibers described above and shown in FIG. 1C. Light may be introduced into the panel through the edge of the panel, for example, by abutting a light source against the edge of the panel. In instances where it is advantageous to locate the panel apart from the light source, a light guide, such as one or more fiber optic strands may be used to convey the light from the light source to the panel. Each of the light guides is affixed to the edge of the panel, for example, by an adhesive or bonding agent. However, joining the light guide to the light panel may be difficult, costly, and lose light in the transfer from the light guide to the panel. Therefore, there is a need in the industry to overcome one or more of the above shortcomings.